This invention relates generally to fluid actuated, percussive, down-the-hole drills, and more particularly to casings that serve as the outer body for such drills.
Fluid actuated down-the-hole drills typically use a system of internal cylinders or feed tubes to perform the fluid conveying or porting functions required of the air cycle. These internal parts must be retained within the central bore of the drill casing. In order to maximize cylinder bore diameter and retain these components in the correct lengthwise position, a retaining snap ring which fits into a groove undercut in the casing is provided as a shouldering means. Manufacturing considerations such as the need for boring, grinding or honing prohibit the formation of an internal shoulder which is part of the casing, or wear sleeve. However, a one-piece casing with an integral shoulder, or a factory installed and non-removable ring, would be desirable to keep the number of serviced parts to a minimum and to avoid damage to this sensitive area during repair servicing.
In addition, it is desirable to provide the casing in a form that it is reversible lengthwise because after the front end of the casing becomes worn and abraded from use at the drilling interface, the casing can be reversed lengthwise to position the unworn casing end at the drilling interface, thereby prolonging the useful life of the casing. Such a reversible casing must provide its snap ring groove with a length greater than the body length of the snap ring, in order to permit installation of the snap ring. Because the snap ring groove is positioned at a location midway between the casing ends, it is a problem for the person assembling the drill to precisely align and insert a snap ring, unless the snap ring groove length is greater than the snap ring body length. However, if the snap ring groove length is too long, for a particular bore and snap ring, the snap ring can become "skewed" or "rotated" and lose its interference fit in the groove, and freely fall out when the casing is empty, as when the drill internal parts are being repaired.
The foregoing illustrates limitations known to exist in present reversible casings. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.